Application of specific electrical fields to spinal nerve roots, spinal cord, and other nerve and bundles for the purpose of chronic pain control has been actively practiced since the 1960s. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of an electrical field to spinal nervous tissue (i.e., spinal nerve roots and spinal cord bundles) can effectively mask certain types of pain transmitted from regions of the body associated with the stimulated tissue. More specifically, applying particularized electrical pulses to the spinal cord associated with regions of the body afflicted with chronic pain can induce paresthesia, or a subjective sensation of numbness or tingling, in the afflicted bodily regions. This paresthesia can effectively mask the transmission of non-acute pain sensations to the brain.
It is known that each region of the human body is associated with a particular spinal nerve root. As shown in FIG. 1, the dermatomes of the human body are mapped, and each dermatome corresponds to a longitudinal spinal position. As can be seen, the head and neck regions are associated with C2-C8, the back is from C2-S3, the central diaphragm is between C3 and C5, the upper extremities are between C5 and T1, the thoracic wall is between T1and T11, the peripheral diaphragm is between T6 and T11, the abdominal wall is associated with T6-L1, lower extremities are located from L2 to S2, and the perineum from L4 to S4. By example, to address chronic pain sensations which commonly focus on the lower back and lower extremities, a specific energy field can usually be applied to a region between bony level T8 and T10. As should be understood, successful pain management and the avoidance of stimulation in unafflicted regions necessarily requires the applied electric field to be properly positioned longitudinally along the dorsal column.
Positioning of an applied electrical field relative to a physiological midline is equally important. Nerve fibers extend between the brain and a nerve root along the same side of the dorsal column as the peripheral areas the fibers represent. Pain which is concentrated on only one side of the body is "unilateral" in nature. To address unilateral pain, electrical energy is applied to the related neural structures lying on the same side of the dorsal column as the afflicted region of the body. Pain which is present on both sides of a patient is "bilateral." Accordingly, bilateral pain is addressed through either an application of electrical energy along a patient's physiological midline or an application of electrical energy about each side of the physiological midline, where in the latter case the electric energy is caused to traverse the critical midline.
Pain managing electrical energy is commonly delivered through electrodes positioned external to the dural layer surrounding a spinal cord. The electrodes are carried by two primary vehicles: the percutaneous catheter and the laminotomy lead.
Percutaneous catheters, or percutaneous leads, commonly have two or more electrodes and are positioned above the dura layer through the use of a Touhy-like needle which passes through the skin, between the desired vertebrae, and opens above the dura layer. For unilateral pain, percutaneous leads are positioned on the afflicted side, as discussed above, and for bilateral pain, a single percutaneous lead is positioned along the patient midline or at least two leads are positioned on each side of the midline. Insertion and positioning of percutaneous leads are typically performed under a local anesthetic.
Laminotomy leads have a paddle configuration and typically possess a plurality of electrodes (for example, two, four, eight, or sixteen) arranged in independent columns. An example of an eight-electrode laminotomy lead is shown in FIG. 2. The illustrated laminotomy lead is a LAMITRODE.RTM. 44 lead manufactured by Advanced Neuromodulation Systems, Inc. of Allen, Tex.
Implanted laminotomy leads are commonly aligned with the physiological midline of a patient. In such position, multiple columns of electrodes are well suited to address both unilateral and bilateral pain, where electrical energy may be administered using either column independently (on either side of the midline) or administered using both columns to create an electric field which traverses the midline.
While the larger size and configuration of laminotomy leads provide increased stability once implanted, laminotomy leads require a surgical procedure for implantation. The surgical procedure, or partial laminectomy, requires the resection and removal of certain vertebral tissue to allow both access to the dura and proper positioning of a laminotomy lead. Unlike the insertion of percutaneous leads, this procedure can result in considerable discomfort for the patient. However, not unlike the use of percutaneous leads, the implanting physician must necessarily rely on patient feedback following trial stimulation to identify at least a proper medial/lateral position of the lead.
The implanting physician has the following alternatives when implanting laminotomy leads: (i) administer a local anesthetic and discuss the positioning of the lead(s) with the patient during an intraoperative trial; (ii) administer an epidural anesthetic and discuss the positioning of the lead(s) with the patient during an intraoperative trial; (iii) place the patient under a general anesthetic, and once the site of implantation is prepared, awaken the patient for an intraoperative trial; or (iv) place the patient under a general anesthetic and position the lead(s) in accordance with a determined anatomic midline of the patient. For (i), the patient is subjected to the greatest discomfort. Accordingly, the value of the feedback provided can be vitiated by the patient's desire to conclude the procedure quickly and inadvertently sacrifice optimization for short-term relief. For alternatives (ii) and (iii), the patient can experience impaired perceptions which can prevent the preferred placement of the lead(s). While alleviating the discomfort of the patient, alternative (iv) is susceptible to the common occasion when the anatomic and physiological midlines are not aligned, thereby preventing optimized medial placement of the lead(s).
Errors in initial lead placement can require additional corrective surgery. As should be appreciated, additional surgeries increase the discomfort of the patient as well as subject the patient and/or the health care system to additional cost burdens.
Consequently, a need exists for a device and method to enable an implanting physician to accurately and quickly position one or more spinal cord stimulating leads while minimizing the operative a discomfort of the patient.